In present residential HVAC (heating, ventilating and air conditioning) systems a 24 volt AC signal is sent from a wall thermostat to a receiving control. The control either reads the signal as ON or the signal is used to directly turn on a 24 VAC electromechanical device. The signal is read as ON or OFF depending on the presence of the 24 VAC with respect to ground. For each function added, e.g., each electromechanical device added, typically at least one new wire is provided.